Banca de QUALIFICAÇÃO: EDSON ALVES DE FRANÇA JÚNIOR

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
DISCENTE : EDSON ALVES DE FRANÇA JÚNIOR
DATA : 19/12/2017
HORA: 09:00
LOCAL: Sala 1 - PPGG
TÍTULO:

Lithochemistry and mineral chemistry of Equigranular High K Calc-Alkaline at the extreme NE of Borborema Province

PALAVRAS-CHAVES:

Equigranular high K calc-alkaline; Litochemistry; Mineral chemistry; Mineralizations; Ediacaran Magmatism

PÁGINAS: 25
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

The Borborema Province consists of large crustal blocks from archaean to paleoproterozoic ages affected by several granites from Ediacaran - Cambrian, represented by batholiths, stocks and dikes. The granitoids of equigranular high K calc-alkaline have been studied in the last years in an individualized way. There is still a lack of integration of
this data at the regional level, with respect to its magmatic affiliation, petrogenetic comparison ( T, P and ƒO2) and evolution of these bodies in the Rio Piranhas-Seridó and São José do Campestre Domains of the Borborema Province. In this context, the data interpreted here showed similarities in terms of petrography and magmatic affiliation, in rocks associated to the Caraúbas, Serra do Lima, Acari and Monte das Gameleiras batholiths, denominated Group I, as in isolated stocks represented by the Serra do Caramuru / Tapuio, Serra da Macambira and Serra da Rajada bodies, called Group II, and also in the form of dikes (Group III). Concern the petrography, all the groups show the similar modal composition, varying from biotite monzogranites to biotite to hololeucocratic to leucocratic sienogranites, with SiO2 between 64.55-75.40% and K2O + Na2O between 7.89 and 9.44%. The felsic paragenesis (> 85%) is formed by quartz, plagioclase and microcline, and mafic by the predominance of biotite (≤10%). The accessory minerals, usually traces, present modal composition ≤1.5%, represented by titanite, opaque, alanite, epitote, zircon, apatite and subordinately fluorite (pluton Caraúbas) and granada (dikes of pluton Serra do Caramuru). Minerals such as chlorite, white mica and carbonate are products of alteration in late-magmatic stages of biotite and feldspar. In general, lithochemistry data shows similarities between the groups, with some particularities among the larger elements. Group II shows a trend towards higher values of Fe2O3, MgO and TiO2 compared to granites from Group I and III. Calculations of the CIPW norm indicates normative minerals of quartz and hypersthene, with compositions of granitoids varying from supersaturated to saturated. The normative plagioclase indicates the granite field in the ternary Ab-An-Or, showing coherence with the modal diagram Q-A-P. The presence of normative corundum mainly for the plutons of groups II and III and diopside (± corundum) normative for Group I, corroborates with the index diagram of Shand, indicating a transitional aluminosity between peraluminous and metaluminous (A/CNK between 0, 87 to 1.08). Harker-type variation diagrams shows negative correlations between Al2O3, CaO, Fe2O3, MgO, TiO2, P2O5, Ba, Sr and Zr, suggesting fractionation of the plagioclase, followed by the mafic as biotite, titanite, apatite and zircon. Rb shows an incompatible behavior, showing late fractionation of K-feldspar in the evolutionary process of magma. Diagrams for rare earth elements (REE) shows enrichment in light REE for groups I and II. They show a ratio of (La / Yb)N between 15.07 and 60.17 for Group I and 8.33 and 35.32 for Group II, indicating a higher concentration of heavy elements in Group I. The negative anomalies of Eu (Eu / Eu * ranging from 0.23 to 0.71) suggest fracture of the plagioclase. The discriminant diagrams of magmatic series show a tendency for a transitional evolutionary trend between alkaline and calcium-alkaline, being classified as high K calcalkaline, with some plutons of Groups I and III prone to a trend of more alkaline nature. Mineral chemistry data (biotite, plagioclase and titanite) were obtained from the literature only for the Group I. The biotite suggests different groups, with values of #fe [Fe / (Fe + Mg)] ranging from 0.715-0.736 (pluton Caraúbas) and 0.532-0.574 (Acari and Monte das Gameleiras plutons), both primaries, belonging to the anita molecule field. Cationic substitutions are of the anita-phlogopite type. The ratio # fe / Al (t) shows that the two groups belong to the magnetite-series. The magmatic association diagrams indicate that the biotite presents a
transitional characteristic between peraluminous-calc-alkaline. Titanite shows similarities between TiO2 and CaO, with differences only in Al2O3 (2.39-4.32%) between the two groups, suggesting magmatic origin. Coupled substitutions shows negative correlations between Ti and Al + Fe, with values ranging from 0.81-0.85 cpfu and 0.15-0.21 cfufu, respectively. The plagioclase shows composition in the field of the oligoclase (An10-28%). In the studied region there are several mineralization occurrences, such as the skarn type W-Mo mineralizations ranging from 510 ± 2 Ma to 554 ± 2 Ma, obtained by the Re-Os method in molybdenite. Recent data on U-Pb in zircon showed that the leucogranites present ages much closer to the mineralizations (561 ± 4 Ma). In this way, it is intended, albeit preliminary, to make comparisons between the studied bodies and their possible relations with the mineralized regions, based on the data of trace elements and correlations with possible sources for mineralizations.

MEMBROS DA BANCA:
Interno - 080.368.454-15 - ANTONIO CARLOS GALINDO - UFRN
Interno - 2042352 - FREDERICO CASTRO JOBIM VILALVA
Presidente - 1513243 - MARCOS ANTONIO LEITE DO NASCIMENTO